Proceedings of XXIII Indian Colloquium on Micropaleontology and Stratigraphy and International Symposium on Global Bioevents in Earth’s History
Sediment Characteristics and Foraminiferal Distribution in the Bet Zone of the Great Rann of Kachchh, Western India
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Published:January 01, 2013
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Nitesh Khonde, D. M. Maurya, A. D. Singh, Archana Das, L. S. Chamyal, 2013. "Sediment Characteristics and Foraminiferal Distribution in the Bet Zone of the Great Rann of Kachchh, Western India", Proceedings of XXIII Indian Colloquium on Micropaleontology and Stratigraphy and International Symposium on Global Bioevents in Earth’s History, N. Malarkodi, Gerta Keller, A. N. Reddy, B.C. Jaiprakash
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Abstract :
Based on geomorphological characteristics, the vast, flat saline tract of the Great Rann of Kachchh is considered as a raised floor of a former gulf that was connected to the Arabian Sea in the west. In general, the Rann exhibits a unique supratidal environment complicated by alternating periods of marine and freshwater inundation and extreme dryness. The Great Rann is divisible into four distinct geomorphic domains – the Banni plain, the Linear trench zone, the Great barren zone and the Bet zone. Contrary to the rest of the Great Rann, the Bet zone shows distinct variations in elevation due to the presence of bets (islands) and is dotted by several vegetated elevated areas, seasonal short distance channels and local depressions. The present study attempts to characterize the environmental conditions of the Bet zone comprising the northwestern part of the Great Rann. Surface sediment samples were collected by digging small pits in the Rann surface at several locations along ESE-WNW and roughly N-S oriented transects (transect 1 and 2). The samples were subjected to detailed grain size analysis and micropalaeontological analysis for determining foraminiferal assemblage. Overall, the sediments of the Bet zone are of sandy-silty to clayey-silty in nature. The grain size was found to vary in accordance with the microgeomorphic setting of the stations. The foraminiferal assemblages recorded along the two transects belong to twelve genera (Ammonia, Elphidium, Bolivina, Nonian, Bulimina, Cibicides, Helenina, Brizalina, Globigerinella, Globigerina, Globorotaloides Gallitellia). Presence of some reworked foraminiferal tests suggests the transport of foraminifera from the Arabian Sea water surges under the influence of strong SW monsoon winds. However, the relatively higher diversity near the open ocean gets reduced in the Great Rann due to the typical hypersaline conditions, submergence patterns, mixing by fresh water (runoff, fresh water influx), and the microenvironments created by variations in the elevation of the Rann surface. The diversity is limited to the few tolerant taxa which can survive through such large scale changes in the environmental parameters.